This invention relates to carriage assemblies and, more particularly, to carriage assemblies for transporting a print member along a predetermined path adjacent a support member.
Carriage assemblies of the above general type have been used for decades in connection with printers and typewriters. The print members utilized over the years have included type bars, type balls, wire matrix print heads and, most recently, print wheels. The most common form of print wheel now in use is the so-called "daisy wheel" which is characterized by a plurality of character elements supported on a respective plurality of spokes extending radially from a central rotatable hub. Examples of printers which include "daisy wheel " wheel print wheels are the HyType I and HyType II serial printers manufactured by Diablo Systems, Inc. of Hayward, California, and an example of an electronic typing system utilizing a "daisy wheel" printer is the Xerox 800 electronic typing system manufactured by the Xerox Corporation of Dallas, Texas.
In contemporary electronic printers utilizing print wheels, provision must be made not only for controlled rotation of the print wheel when located at a first or printing position adjacent the support platen, but also for movement of the print wheel as a unit between such printing position and a second or loading position spaced sufficiently from the platen so that the print wheel may be manually removed from the carriage and replaced with a different wheel. This might be necessary if the print wheel has become worn during prolonged use, or where a print wheel bearing a different font of characters is desired for printing.
Accordingly carriage assemblies used in contemporary print wheel type printers have generally included a first carriage section mounted adjacent the support platen on a pair of rails for movement along a predetermined path parallel to the axis of the platen. The print wheel is coupled to the shaft of a drive motor which is mounted to a second carriage section. The second carriage section is, in turn, pivotably mounted to the first section for movement between first and second positions respectively corresponding to the printing and loading positions of the print wheel. A latching mechanism is normally employed to retain the second carriage section at its first and second positions.
The latching mechanisms most often used have suffered from a number of disadvantages. First, they are subject to jamming when restoring the print wheel to its printing position. Second, the printer might accidentally be operated without the latch being closed and thereby cause print failure and possible part damage. Third, the latching mechanisms are relatively complex and costly.
It would be desirable, therefore, to provide a more effective means of retaining the print wheel in each of its two positions, i.e., printing and loading, which is substantially free of the above-mentioned disadvantages.